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Parasitic Meningitis

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Causes

Primary amebic meningoencephalitis (PAM) is a very rare form of parasitic meningitis that causes a brain infection that is usually fatal. The parasite enters the body through the nose and is caused by the microscopic ameba (a single-celled living organism) Naegleria fowleri.

Risk Factors

Naegleria fowleri is found around the world. In the United States, the majority of infections have been caused by Naegleria fowleri from warm freshwater located in southern-tier states.1 The ameba can be found in:

Water heaters. Naegleria fowleri grows best at higher temperatures up to 115°F (46°C) and can survive for short periods at higher temperatures.2, 3

Soil

Naegleria fowleri is not found in salt water, like the ocean.

Transmission

Naegleria fowleri infects people by entering the body through the nose. This typically occurs when people go swimming or diving in warm freshwater places, like lakes and rivers.1 The Naegleria fowleri ameba travels up the nose to the brain where it destroys the brain tissue.

You cannot be infected with Naegleria fowleri by drinking contaminated water. In very rare instances, Naegleria infections may also occur when contaminated water from other sources (such as inadequately chlorinated swimming pool water or contaminated tap water) enters the nose, for example when people submerge their heads or cleanse their noses during religious practices4, 5, and when people irrigate their sinuses (nose) using contaminated tap water6.

The Naegleria fowleri ameba causes primary amebic meningoencephalitis (PAM) when it travels up the nose to the brain and destroys the brain tissue. Naegleria fowleri infections are very rare. In the 10 years from 2003 to 2012, 31 infections were reported in the U.S. All were fatal.

Signs and Symptoms

Naegleria fowleri causes the disease primary amebic meningoencephalitis (PAM), a brain infection that leads to the destruction of brain tissue. In its early stages, symptoms of PAM may be similar to symptoms of bacterial meningitis.

Initial symptoms of PAM start 1 to 7 days after infection. The initial symptoms include headache, fever, nausea, vomiting, and stiff neck. Later symptoms include confusion, lack of attention to people and surroundings, loss of balance, seizures, and hallucinations. After the start of symptoms, the disease progresses rapidly and usually causes death within about 5 days (range 1 to 12 days).

Diagnosis

PAM is rare. The early symptoms of PAM are more likely to be caused by other more common illnesses, such as bacterial or viral meningitis. People should seek medical care immediately whenever they develop a sudden onset of fever, headache, stiff neck, and vomiting, particularly if they have been in warm freshwater recently.

Treatment

Several drugs are effective against Naegleria fowleri in the laboratory. However, their effectiveness is unclear since almost all infections have been fatal, even when people were treated.

Prevention

Naegleria fowleri infects people when water containing the ameba enters the body through the nose. Infection is rare and typically occurs when people go swimming or diving in warm freshwater places, like lakes and rivers. Very rarely, infections have been reported when people submerge their heads, cleanse their noses during religious practices, or irrigate their sinuses (nose) using contaminated tap or faucet water. Naegleria fowleri can grow in pipes, hot water heaters, and water systems, including treated public drinking water systems.

Personal actions to reduce the risk of Naegleria fowleri infection should focus on limiting the amount of water going up the nose and lowering the chances that Naegleria fowleri may be in the water.

Please visit the following pages for information on lowering your risk of infection in specific situations: